1. Technical Field of the Invention
The present invention relates to packet communications traffic and, in particular, to cryptographically signing packet traffic and, even more specifically, to the use of steganographic techniques to hide authentication information in packet communications.
2. Description of Related Art
The Greek term “steganography” refers to the art and science of hiding the existence of information using various secret “hidden writing” communication techniques that allow important messages to be securely carried over insecure communications channels. Steganography achieves confidentiality with respect to a transmitted secret message by hiding that message inside of a larger context. In this way, the secret message is kept from someone who is not supposed to read the message because they neither know how to read it, nor even recognize it is present in the context. Someone who is supposed to read the message, however, possesses a key that permits the message to be both detected in the context and read.
Steganographic techniques have, in the past, been primarily associated with, for example, invisible inks, messages sent via telephone line noise, and red cellophane such as that used in games to reveal information hidden in a red-blue block. More recently, steganographic techniques have been used in the computer environment to hide information in graphical images, sound files, text files, or other media.
An important characteristic of a steganography process is imperceptibility. By this it is meant that the existence of a stenographically hidden message should not be readily apparent from a review of the carrying media (i.e., the context). More generally, the media in which the message is hidden should not draw any attention to itself in a way that makes the perceiver suspicious of hidden content. Thus, the goal of steganography is to hide messages inside other “harmless” messages in a way that does not allow any enemy to even detect that there is a second secret message present.
Most common steganography techniques lose their security when the steganographic operation of the process (i.e., its key) is known, and thus should be used together with key based encryption for additional security. A good steganography process should therefore fulfill the cryptographic “Kerckhoff principle” requirement. In this context, one assumes that the “enemy” has full knowledge of the design and implementation details of the steganographic process. Security is then provided for the process by means of a short, easily exchangeable, secret key, the knowledge of which is required by the enemy in order to obtain the hidden information.
By combining the Kerckhoff requirement with the imperceptibility characteristic, an ideal steganography process should be designed in a manner such that the enemy has very little chance of becoming suspicious that hidden information is present and, without knowledge of the secret key, no chance of actually being able to recover that hidden information.
With the development of the Internet for linking computers, and the evolution of the Internet protocol (IP) for defining how messages are communicated between linked computers, a need had arisen for using packets as a media for conveying hidden information. The present invention addresses that need in particular as well as other needs concerning the communication of packetized information that are recognized by those skilled in the art.